So, I checked for updates and it reported software up to date. On investigation I discovered it was on release candidate channel, so I switched to devel channel and it downloaded 532mb of updates.
I installed the updates and after a couple of trys, I managed to coax it to boot.
Deep joy, it booted into staged mode! So pleased with the result. I am typing this on my Lenovo tab.
Thank you so much for working your magic. ☺